On the pass- and stop-band optical filtering by passive silicon photonic circuits using square-layout MZI ring(s)

Silicon photonic square-layout ring resonator-based circuits comprising Mach–Zehnder interferometers (MZIs), grating couplers, three-port splitters and combiners were designed, modeled, and fabricated for efficient control over the stop-band and pass-band filtering of transmission spectrum. It was found that exploiting square-layout rings and assigning an MZI (called the master MZI) to the grating couplers of the used photonic circuits allow engineering the optical stop-band, creation of multi pass-band and the quality of filtering. Excluding the master MZI and using only single square-layout ring of MZIs would yield a two-lobe spectrum having a sharp narrow stop-band at 1542 nm wavelength, whereas with a two-ring configuration, its width extends up to 20 nm. Furthermore, including the master MZI within the circuit configuration eliminates lobes from the transmission spectrum and recreates a single lobe with large bandwidth and almost low ripple over the hat of the lobe. The optical response of the photonic circuit containing both the two-ring and master MZI leads to the formation of a single pass-band with an almost flat-hat lobe.